Stripper for shell drawing dies



April 4, 1944. s NEWELL 2,345,857

STRIPPER FOR SHELL DRAWING DIES Filed March 6, 1943 2 SheetsSheet 1 ATTORNEYS E395 E W2 April 4, 1944. L, NEWELL I 2,345,857

' STRIPPER FOR SHELL DRAWING DIES Filed March 6, 1943 2 Sheets-Sheet 2 2P jj Tj Big. E1. 22/12 %-27 I 7 I? ll 1 INVENTOR BY L. SNEWELL.

i ATTORNEYS 7 Patented Apr. 4, 1944 STRIPPER FOR SHELL DRAWING DIES Lester S. Newell, Boulder, $3010., assignor to Remington Arms Compan a corporation of Dela y, Ina, Bridgeport, Conn., ware Application March 6, 1943, Serial No. 478,249

11 Claims.

The present invention relates to a tube drawing apparatus for the forming of tubular or shell shaped articles, and particularly to stripper mechanism means employed in such apparatus for removing the drawn articles from the punch during the upstroke of the punch following the passage of the article through the drawing die. While the apparatus is adapted for the drawing of any type of tubular article, the present description is by way of example directed to the drawing of cartridge cases, which in the course of manufacture are subjected to a series of drawing, annealing, and trimming operations,

and which fromtheir nature require the highest precision standards, both from the standpoint of dimensions and metal characteristics.

In drawing a tubular article, such as a cartridge case, the cup-shaped blank is engaged upon a punch and forced through a drawing die of larger diameter than the punch and smaller diameter than the blank so that the wall of the case is drawn to substantially the thickness of the space between the punch and the die. The metal of the article tends to flow as its well thickness is decreased and its length increased, and while the wall thickness is uniform it is found in practice that at some point or points about the punch the metal will flow to a greater extent than at others, this being in part due to the impossibility in production manufacture of maintaining perfectly polished surfaces upon the punch and die, and in part due to unbalanced bending moments and stresses set up in the machine under the extreme load required in the drawing operation. This results in an uneven edge at the mouth of the case, characterized by certain points being higher than others, this uneven edge being trimmed in a later operation.

In stripping the case from the punch the stripper means engages the punch above the mouth edge of the case, after the latter is forced through the die, and through the upstroke of the punch the case is stripped from the punch. With previous types of stripper means a case havin such a high point at the mouth edge would be en gaged only at this high point by the stripper means, and consequently the abnormal load applied at the high point would set up stress concentrations in the metal causing it to distort and crack. If undetected, cracks in cartridge cases may result in serious damage through splitting of the cases upon firing. The stripping force required to remove the cases from the punch is of a very high order, thi being due to the fact that the case is actually smaller in its inside dimension after stripping than it was while on the punch, which results from the circumstance that the elastic properties of the case and the punch may be almost identical, the case during its draw being stressed into its plastic range and while going through the die transmits stresses to the punch and die. As a result, the punch is necked down at this moment and actually draws a case the size of the necked down area of the punch. The punch in restoring itself to its original dimension actually expands itself inside the case, hence requiring an extremely high stripping pressure to remove it.

It is an object of the present invention to provide stripper means comprising a plurality of relatively movable members arranged to engage about the punch and to have relative axial movement with respect to each other, so that the several stripper members will engage points about the entire circumference of the mouth of the case from the highest to the lowest points, thus distributing th stripping pressure and preventing the concentration of stresses upon only one point of the mouth.

Another object is to provide stripper means having a relatively free expansive and contractive action so that during the drawing operation the drawn case may be passed therethrough without any chance of damaging its surface through forcefu1 contact of the stripper members therewith.

A further object is to provide stripper means arranged to engage the surface of the punch above the drawn case, following the drawing operation, in combination with positive wedge means for retaining the stripper members in engagement with the punch, so that the removal of the case from the punch will be positive. Fail" ure to remove a drawn case from the punch may result in delayed production and expensive tool damage.

With the above and other objects in view, an

embodiment of the invention is shown in the Fig. 2 is a horizontal sectional view, taken along the line 2-2 of Fig. 1, showing the stripper means in top plan and partially broken away.

Fig. 3 is a plan view, on an enlarged scale, of one of the segmental stripper members, and showing diagrammatically in dot-and-dash lines the cooperation of the bearing surfaces of this member with the bearing surface of the stripper ring.

Fig. 4 is a side elevation of one of the segmental stripper members.

Fig. 5 is a fragmentary vertical sectional view, showing an advanced position of the punch wherein the drawn case is engaged with the stripper means.

Fig. 6 is a fragmentary vertical sectional view, showing the completed drawn case disposed below the stripper means in stripping relation therewith at the beginning of the upstroke of the punch.

Fig. 7 is a horizontal sectional view, taken alon the line 1-1 of Fig. 6, and showing the stripper means in bottom plan,

Fig. 8 is a side elongation of -a cartridge case of the type adapted to be drawn and stripped by the apparatus of the invention.

Similar reference characters indicate corresponding parts throughout the several parts of the drawings.

Referring to the drawings, the tube drawing apparatus, of the punch and die type illustrated by way of example in the present disclosure, comprises a die holder IU provided in itsupper side with a cylindrical pocket H .in-which is positioned the drawin die block l2 of conventional shape, having the contracted lower end of its die passage l3 substantially registering with a central passage l4 through the die holder. A centrally apertured retaining plate I5 is secured at the upper side of the die holder to retain the die block in place. While only one die block isillustrated it will be understood that a series of such blocks may be employed, stacked one on another in accordance with standard practice in .the drawing of metal tubes.

In the lower side of the die holder there isprovlded a cylindrical pocket l6, within which the stripper means is engaged, as will presently more fully appear, the lower side of this pocket being formed by a bearing plate I'I, secured to the underside of the die holder, and provided with a central passage I8 of somewhat larger diameter than the passage I3 through the die block.

The reciprocating punch I9 is adapted to move downwardly through the die during the drawing operation upon the tubular or shell-shaped article, illustrated as a cartridge case blank A, and to carry the drawn case downwardly below the stripper means, whereupon it is stripped from the punch during the upstroke of the latter.

The stripper means comprises a stripper holder ring member 20 disposed in the pocket 66 having a cylindrical outer wall of substantially smaller diameter than the diameter of the pocket 26 and so fitted within the pocket that it may have free floating lateral movement therein. The opening 2i through the stripper holder ring is in the form of a frustum of a cone tapering inwardly from the bottom to the top of the ring. Within the ring opening, and normally supported ,upon the bearing plate ll forming the bottom of the pocket it, there is disposed a sectional expan sion and contraction stripper element comprising six segment members 22, each provided upon its inner periphery with a downwardly and inwardly tapered guide or lead surface 23 terminating in a cylindrical punch-engaging wall 24 at its lower end, and each provided in its outer periphery with a laterally disposed spring-receiving groove 25, which with the similar grooves of the other segment members constitute a circumferential expansion and contraction groove. Within this groove there is engaged the helically wound spring 26, adapted normally to draw the segment members into their contracted position, as shown in Figs. 1 and 2, and to permit free expansion of the ring through the engagement of the cartridge case or punch therethrough as shown in Figs. 5 and 6. 0

The outer periphery of'the stripper device is tapered inwardly from bottom to top at the same angle as the taper of the opening 24 of the stripper holder ring 20 and its diameter is such that in the contracted position, as shown in Figs. 1 and 2, there is sufficient clearance in the opening 2| to permit of expansion by engagement therein of the drawn case, as shown in Fig. 5, without binding engagement with the wall of the opening 2|. The height of the segmental stripper members is substantially less than the height of the ring 20 to permit of substantial vertical displacement of the stripper members within the opening 2! during the stripping operation, as will presently more fully appear.

The outer peripheral surfaces of the stripper members are substantially in the form of a frustum of a pyramid, each segment member 22 being provided at its outer periphery and along the line of its central vertical plane with relatively small bearing surface areas 21 and 28, respectively below and above the spring receiving groove 25, the surfaces 29-29 and 3030 at each side of these bearing areas extending as straight flat bends to beveled end surfaces 3l-3I and 32-32 extending to the vertical radially disposed end surfaces. The length and angles of the band surfaces are such that in any position of adjustment of the segment member between the bottom and top of the ring opening 2|, the bearing surfaces 2'! and 28 will be in bearing contact with the wall of the opening, while the outer end corners of the surfaces 2929 and 30-30 remain out of contact, these corners being clear of both the small diameter high plane of the bearing opening 2| in a raised position of the segment member, as indicated diagrammatically by the short dot-dash lines in Fig. 3, and clear of the large diameter low plane in a relatively lower position of the segment member, as indicated by the long dot-dash lines in Fig. 3.

The segment members are so designed that when in stripping engagement with the surface of the punch, as shown in Figs. 6 and 7, the inner peripheral surface 24 is concentric to and of the same diameter as the surface of the punch, the end walls of the segment members in this full-engaging stripping position being spaced from each other.

In operation, the punch with the cartridge case component thereon is moved downwardly through the die, the wall of the case being drawn between the punch and the die to a wall thickness corresponding substantially to the annular space between the punch and the die. As the case moves downwardly below the die it passes through the sectional segmental stripper which expands through the yieldability of the spring 26, as shown in Fig. 5. the drawn case moving below the stripper. As the punch completes its downward stroke, movement of the upper edge or the case below the stripper causes the segment members to contract into engagement with the surface or the punchabove the case, as shown in Figs. 6 and 7. As above pointed out, the drawing action is such that the mouth edge B is frequently drawn to a greater height at one point than at another point, this edge being illustrated as high at one point and low at the diametrically opposite point and inclined between these points, this being a very common form of mouth edge formation.

As the punch starts its upstroke, the mouth edge 01 the cartridge case is brought into engagement with the underside of the sectional stripper element, the high point engaging the segment member directly above it and the lower points engaging the segment members above these points. As the stripper holder ring 20 has considerable clearance in the pocket I 6 of the die holder the ring is allowed to float sidewise to an eccentric position within the pocket, being controlled in this floating movement bythe pressure of the segment members of the stripper element transmitted from the mouth edge of the cartridge case through the segment members to the stripper holder ring. It yvill be evident that this floating of the stripper holder ring allows the segment members to align themselves along the plane delineated by the mouth of the case, the segment members moving axially relatively to each other within the tapered opening of the float ng ring in conformity with the edge of the case. This enables the several stripper segment members to contact. the mouth of the case and exert a force, practically uniform, along or around the entire mouth of the case, thus preventing the severe stress to a single point, the high point, that re sults in the use of a stripper means capable of engaging the high point only of the mouth of the case. In any position of the several segment members within the opening 2| the bearing surfaces 21 and 28 match the bearing surface in the ring opening so that during the stripping action the segment members are firmly retained against both axial upward movement away from the case and lateral movement away from the punch, thus insuring positive removal of the case.

The form of the invention illustrated in the drawing and described herein is typical-and illustrative only, and it is evident that the invention is capable of embodiments in other forms, all falling within the scope of the appended claims, which are to be broadly construed.

What is claimed is:

1. In a drawing punch and die apparatus, stripper means comprising a plurality of separable circumferentially arranged stripper members assembled as a unitary element adapted to engage about the punch adjacent the mouth edge of the drawn article, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn article.

2. In a drawing punch and die apparatus, stripper means comprising a plurality of separable c'lrcumferentially arranged stripper members assembled as a unitary element adapted to engage about the punch adjacent the mouth edge of the drawn article, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn article, and annulus cooperating with said stripper element to retain said stripper members in their axially moved stripping relation with said punch.

3. In a drawii'ig punch and die apparatus, stripper means comprising a sectional segmental stripper element having an axial opening therethrough for receiving the punch and drawn article thereon, and characterized by a plurality of separable circumferentially arranged segment stripper members assembled as a unitary element adapted to engage about the punch adjacent the mouth edge of the drawn article, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn article, and stripper holder ring means surrounding said stripper element adapted to cooperate therewith to retain said stripper members in their axially moved stripping relation with said punch.

4. In a drawing punch and die apparatus. stripper means comprising a sectional segmental stripper element having an axial opening there through for receiving the punch and drawn article thereon, and characterized by a plurality of separable circumferentially arranged segment stripper members assembled as a unitary element adapted to engage about the punch adjacent the mouth edge of the drawn article, spring means yieldably retaining said stripper members in assembled relation about said axial opening, said members being axially'movable relatively to each other in conformity with the mouth edge of the ,drawn article, and holder means cooperating with said stripper element to retain said stripper members in their axially moved stripping relation with said punch.

5. In a drawing punch and die apparatus. stripper means comprising a sectional segmental stripper element having an axial opening therethrough for receiving the punch and drawn article, and including a plurality of circumferentially arranged segment stripper members adapted to engage about the punch adjacent the mouth edge of the drawn article, said members being axially movable relatively to each other in conform ty with the mouth edge of the drawn article, and stripper holder ring means surrounding said stripper element having its opening tapered inwardly in the direction of disengagement of said punch from the drawn article adapted to be engaged by said stripper members in the r axially moved stripping relation with said punch.

6. In a drawing punch and die apparatus. stripper means comprising a sectional segmental stripper element having an axial opening therethrough for receiving the punch and drawn article, and characterized by a plurality of separable circumferentially arranged segment stripper members assembled as a unitary element adapted to engage about the punch adjacent the mouth dge of the drawn article, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn article, and stripper holder ring means surrounding said stripper element having lateral shifting movement relatively to the axis of said stripper element, and adapted to be engaged and laterally shifted by said stripper members in their axially moved stripping relation with said punch.

7. In a drawing punch and die apparatus. stripper means comprising a sectional segmental stripper element having an axial opening therethrough for receiving the punch and drawn article, and including a plurality of circumfe entially arranged segment stripper members adapted to engage about the punch adjacent the mouth edge of the drawn article, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn article, and stripper holder ring means surrounding said stripperelement having its open-- ing tapered inwardly in the direction of disengagement of said punch from the drawn article, and having lateral shifting movement relatively to the axis of said stripper element, and adapted to be engaged and laterally shifted by said stripper members in their axially moved stripping relation with said punch.

8. In a drawing punch and die apparatus, stripper means comprising a sectional segmental stripper element having an axial opening therethrough for receiving the punch and drawn article, and including a plurality of circumferentially arranged segment stripper members adapted to engage about the punch adjacent the mouth edge of the drawn article, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn article, and stripper holder ring means surrounding said stripper element having its opening tapered inwardly in the direction of disengagement of said punch from the drawn article adapted to be engaged by said stripper members in their axially moved stripping relation with said punch, said stripper members each having upon their outer periphery a centrally disposed bearing area parallel to and adapted to engage the wall of said ring opening and clearance surfaces at each side adapted to not engage the wall of said ring opening.

9. In a drawing punch and die apparatus, stripper means comprising a sectional segmental stripper element having an axial opening therethrough for receiving the punch and drawn article, and including a plurality of circumferentially arranged segment stripper members adapted to engage about the punch adjacent the mouth edge of'the drawn article, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn article, and stripper holder ring means surasaasw ing tapered inwardly in the direction of disenrounding said stripper element having its opengagement of said punch from the drawn article and having lateral shitting movement relatively to the axis of said stripper element, and adapted to be engaged and laterally shiited by said stripper members in their axially moved stripping relation with said punch, said stripper members each having upon their outer periphery a centrally disposed bearing area parallel to and adapted to engage the wall of said ring opening and clearance surfaces at each side adapted to not engage the wall of said ring opening.

10. In a cartridge case drawing punch and die apparatus, stripper means comprising a sectional stripper element including a plurality of separable circumferentially arranged stripper members assembled as a unitary element adapted to engage about the punch adjacent the mouth edge of the drawn cartridge case, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn cartridge case, and laterally shiftable holder means cooperating with said stripper element to retain said stripper members in their axially moved stripping relation with said punch.

11. In a cartridge case drawing punch and die apparatus, stripper means comprising a sectional stripper element including a plurality of circumferentially arranged stripper members adapted engage about the punch adjacent the mouth edge of the drawn cartridge case, said members being axially movable relatively to each other in conformity with the mouth edge of the drawn cartridge case, and a laterally shiftable holder ring surrounding said stripper element having its opening tapered inwardly in the direction of disengagement of said punch from the, drawn cartridge case and adapted to be engaged and shiftedby said stripper members in their axially moved stripping relation with the punch.

LESTER S. NEWELL. 

